The invention relates to a kneader-mixer for performing mechanical, thermal and/or chemical processes. Kneader-mixers of this type are e.g. known from Austrian Pat. No. 294020 and Swiss Pat. No. 410789. In these known kneader-mixers a kneading shaft with vertically fitted disk elements is cleaned on radial kneading counterelements fixed in the casing, the kneading shaft with the disk performing an axial reciprocating movement to ensure good cleaning. The time involved in this reciprocating movement leads to poor cleaning of the heat transferring surfaces, i.e. to an inadequate heat exchange and an inadequate kneading action, despite high energy expenditure. In another kneader-mixer according to German Pat. No. 23 49 106 the heat transferring disks are also fixed to the shaft and are cleaned by hooks during a rotary movement, a good kneading action being obtained through the co-operation between mixing bars on the disks and the hooks fixed in the casing. The disadvantage of this arrangement with regards to certain products is the formation of toroidal product accumulations between the disks, which greatly inhibit the movement of material between said disks.